Periodic Reporting for period 4 - ConTROL (Charge-TRansfer states for high-performance Organic eLectronics)
Periodo di rendicontazione: 2025-01-01 al 2025-12-31
Thin films comprising a blend of electron donating and electron accepting molecules are ubiquitous in organic opto-electronic devices. At the donor-acceptor interfaces, intermolecular charge-transfer (CT) states form, in which an electron is transferred from donor to acceptor. Electrical doping involves CT in the ground-state, from dopant to host, and results in increased conductivities of the host organic semiconductor. Furthermore, efficient photo-induced charge generation in organic materials depends crucially on donor-acceptor interfaces where the CT state is an excited state. Organic electronics will in the future enable new applications for a healthy, green and connected society, such as for example low-cost, non-toxic and building integrated and indoor photovoltaics, efficient light sources, sensors for healthcare or artificial synapses. However, current progress is hampered by a lack of understanding of the fundamental properties of intermolecular CT states and their dissociation and decay mechanisms. Improving performance of devices is nowadays often based on time consuming rail-and-error methods. The objective of ConTROL is to fill the knowledge gap and link device performance to CT state properties and molecular parameters of donor and acceptor. Besides the established way of tuning electro-optical properties by molecular design and appropriate donor-acceptor selection, innovation in ConTROL lies in the use of weak and strong interactions with the opto-electronic device’s optical cavity. The newly developed models and simulation code taking these effects into account, from the molecular to the device level. The project will demonstrate rational design of new organic semiconductors resulting in improved performance of organic electronic applications, as well as novel device concepts for sensing and energy conversion based on donor-acceptor blends.
The objectives of ConTROL require state-of-the-art organic thin film and device fabrication and characterization facilities, which have been built up at the start of the project. Together with the existing synthetic chemistry expertise, the lab now combines high-throughput solution and vacuum deposition tools and expertise for the fabrication of new donor-acceptor systems and devices. Optical and electrical models have been implemented and have throughout the project aided in the design and synthesis of new donor-acceptor materials as well as device optimization. These facilities have enabled the ConTROL team to generate fundamental knowledge in the field of organic electronics, applicable to current and future donor-acceptor systems and devices based hereupon. Specifically:
- We have revealed how the non-radiative decay mechanisms at the donor-acceptor interface set an upper limit for the achievable detectivity of organic photodetectors.
- We have elucidated how the molecular factors which affect the radiative and non-radiative decay properties also affect the lineshape of the emission spectra of neat materials and donor:acceptor blends, providing design rules for donor:acceptor systems with improved device performance.
- The coupled electro-optical models developed within ConTROL have been used to design device architectures for organic indoor photovoltaics and resonant cavity device architectures in which we can manipulate donor, acceptor and CT absorption, red-shifting or increasing the absorption strength by more than a factor of 10 at specific wavelengths. In combination with targeted material synthesis, this allows us to demonstrate organic narrowband photodetectors with extended detection wavelengths.
- The project team has demonstrated several new device concepts: Our understanding on ground-state CT (doping) achieved within ConTROL has enabled efficient narrowband near-infrared photo-detection by doping a donor-acceptor blend as well as organic thermal detectors based on molecularly doped polymers. A new device concept and design principles for photon energy up-conversion was proposed as well.
These results were published in over 30 publications in international peer-reviewed journals, presented at over 15 international conferences.
- We have revealed how the non-radiative decay mechanisms at the donor-acceptor interface set an upper limit for the achievable detectivity of organic photodetectors.
- We have elucidated how the molecular factors which affect the radiative and non-radiative decay properties also affect the lineshape of the emission spectra of neat materials and donor:acceptor blends, providing design rules for donor:acceptor systems with improved device performance.
- The coupled electro-optical models developed within ConTROL have been used to design device architectures for organic indoor photovoltaics and resonant cavity device architectures in which we can manipulate donor, acceptor and CT absorption, red-shifting or increasing the absorption strength by more than a factor of 10 at specific wavelengths. In combination with targeted material synthesis, this allows us to demonstrate organic narrowband photodetectors with extended detection wavelengths.
- The project team has demonstrated several new device concepts: Our understanding on ground-state CT (doping) achieved within ConTROL has enabled efficient narrowband near-infrared photo-detection by doping a donor-acceptor blend as well as organic thermal detectors based on molecularly doped polymers. A new device concept and design principles for photon energy up-conversion was proposed as well.
These results were published in over 30 publications in international peer-reviewed journals, presented at over 15 international conferences.
New material and device concepts for organic photodetectors, improving upon the current state-of-the-art have been demonstrated experimentally and described. The improvements beyond the state of the art lie in the extension of the wavelength range, deeper into the near infrared, while keeping a high performance. Performances achieved are benchmarked against a newly derived theoretical limit, allowing identification of further pathways for improvement. Novel device concepts for organic photodiodes, as well as thermal and photon up-conversion based on donor:acceptor blends have been reported on. Further development of these devices for targeted applications lies outside the scope of this project, which has established their theoretical framework and first demonstration on lab-scale.
The ConTROL team has further developed a new method for an accurate measurement of the photoluminescence quantum efficiency improving the measurement accuracy by a factor of 10 as compared to classical measurement techniques. Our experience in photo-thermal deflection spectroscopy, built up in the first half of the project, was crucial in this development.
The ConTROL team has further developed a new method for an accurate measurement of the photoluminescence quantum efficiency improving the measurement accuracy by a factor of 10 as compared to classical measurement techniques. Our experience in photo-thermal deflection spectroscopy, built up in the first half of the project, was crucial in this development.